Security nuts

Abstract

A security nut, which can be tightened on to a bolt but not slackened, has a body which is dome shaped and through which a threaded bore passes. The external dome-shaped surface of the body is provided with grooves which have diverging walls which can be engaged by driving faces of a socket tool to tighten the nut but not to slacken it. The dome-shape of the body makes it virtually impossible to grip it to slacken the nut.

I claim: 
     
       1. A security nut comprising a body having opposite ends of greater and lesser diameter respectively and an external surface of generally domed shape between said ends, a threaded bore extending between said ends, and a plurality of grooves in said domed surface and extending substantially between said ends, each groove having a base and two walls, one of said walls of each groove lying in a plane generally radial to the longitudinal axis of the bore and the other of said walls diverging, in a direction away from the base of the groove, from the one wall, the groove walls being so arranged that the nut can be rotated in a tightening sense with respect to the hand of the thread in the bore by torque applied to the nut by engagement of said one walls by driving faces on a suitable tool but so that said inclination of said other walls prevents torque being applied to the nut by engagement of said other walls to rotate the nut in a slackening sense with respect to the hand of the thread in the bore. 
     
     
       2. A nut according to claim 1 in which the diameter of said end of greater diameter is between one and a half and three times the nominal diameter of the thread in the bore. 
     
     
       3. A nut according to claim 2 in which the diameter of said end of greater diameter is approximately twice the nominal diameter of said thread. 
     
     
       4. A nut according to claim 1, in which the domed surface is part-spherical, the spherical radius being approximately equal to the nominal diameter of the thread in the bore. 
     
     
       5. A nut according to claim 1, in which the perpendicular distance between said ends of greater and lesser diameter is between about 0.8 and 0.9 times the nominal diameter of the thread in the bore or on said shank. 
     
     
       6. A nut according to claim 1, in which said ends of greater and lesser diameter are planar. 
     
     
       7. A nut according to claim 1, in which the base of each groove makes an angle of 28° with an imaginary line passing through the base and which is parallel to the longitudinal axis of the thread 
     
     
       8. A security nut comprising a body having opposite planar ends of greater and lesser diameter respectively and an external surface of part-spherical shape between said ends, a threaded bore extending between said ends, the spherical radius of said external surface being approximately equal to the nominal diameter of the thread in said bore, and a plurality of grooves in said external surface and extending substantially between said ends, each groove having a base and two walls, one of said walls of each groove lying in a plane generally radial to the longitudinal axis of the bore and the other of said walls diverging, in a direction away from the base of the groove, from the one wall, the groove walls being so arranged that the nut can be rotated in a tightening sense with respect to the hand of the thread in said bore by torque applied to the nut by engagement of said one walls by driving faces on a suitable tool but so that said inclination of said other walls prevents torque being applied to the nut by engagement of said other walls to rotate the nut in a slackening sense with respect to the hand of the thread in said bore. 
     
     
       9. The combination of a nut and a driving tool, the nut comprising a body having opposite ends of greater and lesser diameter respectively and an external surface of generally domed shape between said ends, a threaded bore extending between said ends, and a plurality of grooves in said domed surface and extending substantially between said ends, each groove having a base and two walls, one of said walls of each groove lying in a plane generally radial to the longitudinal axis of the bore and the other said wall diverging, in a direction from the base of the groove, from the one wall; the tool having a recess to receive said nut, the recess having driving faces to engage said one walls of the grooves, the groove walls being so arranged that the nut can be rotated in a tightening sense with respect to the hand of the thread in sad bore by torque applied to the nut by engagement of said one walls by said driving faces but so that said inclination of said other walls prevents torque being applied to the nut by engagement of said other walls by the tool to allow the nut to be rotated in a slackening sense with respect to the hand of the thread in said bore.